This invention relates to a thermal serial dot printer, in which a thermal head is carried by a carriage movable relative to the paper, which is supported by a flat bar, the head comprising a flat support carrying a column of thermal printing elements disposed on a column transverse to the paper movement.
In known printers, the thermal head is generally carried by a frame pivoted on a shaft, and urged resiliently towards the paper in such a manner as to ensure good contact between the thermal elements and the paper.
The plane of the bar is generally fixed in such a manner that for a determined paper thickness it is parallel to the plane of the head. In the case of dot printing, for example in accordance with normal 7.times.5 dot matrices, because of the relatively limited length of the column of thermal elements, which is equal to the character height, and because of the quality required of the printing, any parallelism error between the head support plane and the plane of the paper therefore has negligible influence on the printing.
In the case of heads with a large number of dots, such as high definition printing heads or heads designed for printing very tall lines, for example for facsimile transmission apparatus, a small parallelism error causes unacceptable non-uniformity in the printing, so that known printers are not suitable for such purposes.
The technical problem which the invention proposes to solve is to create a thermal printer of the aforesaid type, in which the printing uniformity is independent of the number of thermal elements of the column.